Electric condenser



Patented Aug. 4, 1931 UNITED STATES PATENT OFFICE GODFREY STEERUP, '0]?HAYWOOD, ILLINOIS, ASSIGNOR, BY MESNE ASSIGNMENTS, TO AMERICAN ELECTRICCOMPANY, INC., OF CHICAGO, ILLINOIS, A CORPORATION OF DELAWARE ELECTRICCONDENSER No Drawing.

The present invention relates in generalnated paper are in common useand are 1111- doubtedly satisfactory for low voltages, but when used inpower packs for radio or other purposes where voltage peaks of one ormore kilovolts are encountered, they are not satisfactory. For meetingthese higher voltages with a paper condenser, a make-shift- 1 plan is incommon use at the present time which consists in increasing the numberof layers of paper between the electrodes. This procedure doesundoubtedly give a high dielectric strength while the condenser is new,

2 but introduces factors conducive to dielectric breakdown b continueduse of the condenser under liigh voltage.

Many widely different theories have been I voiced to explain the causeof this failure,

but it is generally conceded that every condenser using impregnatedpaper contains reasonably'large quantities of gas and any bubble orlayer. of gas must beregarded as a dielectric in series with thecomposite dielectric on each side of it in a radial direction.Microscopic films and pockets of either gas or moisture are undoubtedlyentrapped within the kinky windings of the capillary ducts in the papermaterial. If it 35 is air, the air pocket will be ionized under theelectric stress following high potential and will elongate with thepoles of the elongation pointing towards the respective electrodes;ionization of any. air pocket or film will, of course, result indielectric breakdown; if microscopicmoisture films are present, thesefilms may also become elongated by the electric field due to theirhigher spe- ClfiO capacity which then forms a conducting 45 bridgeacross the dielectric.

Application filed larch 23, 1929. Serial No. 349,517.

Although special precautions are taken for drying the paper, as well asthe fact that impregnation takes place by the aid of heat,

it is highly improbably that every one of the enormous number of fiberswhich are contained per square foot of insulation is absolutely dry,although the bulk may be; and it is understood, of course, that just asingle duct carrying gas or moisture is sufficient to start the failurein the form of di- H electric breakdown.

Now, taking it for granted that in acondenser it is desirable to have adielectric of a homogeneous, non-fibrous nature, I have invented acondenser for high tension purposes which contains a new dielectric andalso meansfor manufacturing this dielectric in a practical way.

My improved dielectric comprises a main insulating body which issupported on a rel-' atively thin tissue which I term a carrier. As acarrier for my insulation I use very thin gutta percha tissue which inits physical and chemical characteristics is quite different from paper.It is homogeneous and contains no capillaries of any sort. It is nothygroscopic, a property which is characteris tic of all fibrousmaterials. A tissue of pure gum rubber may also be used.

Regardless of magnitude of voltage for which my condenser is to be used,I use only one layer of fine tissue, but reinforce this tissue andmodify its characteristics by treating it with a solution of asphalt.This asphalt insulation may be, built up in layers, thus increasing thethickness of the final insulation, the thickness being dependent uponthe voltage which the condenser is to be operated at. Thus, in mycondenser the main body is not only uniform, perfectly homogeneous,non-fibrous, and chemically and physically stable because of the pureasphalt used, but its carrier is also of a homogeneous, uniform,non-fibrous structure.

To the foregoing characteristics of this insulation is added the veryimportant one of being self-healing under certain conditions. In theordinary paper impregnated condenser the insulation possessespractically no viscosity or plasticity. At normal temperatures, thepin-hole resulting from electric puncture remains, while the insulationin my condenser is plastic and will'seal itself unless conductinconditions are brought about to an extent beyond repair by the closingaction of the asphalt. y

In order to make this new insulation, I do this: I dissolve pure asphaltin carbon tetrachloride or in gasoline, or in an solvent which is commonto the gutta perc a and to the asphalt as well. The result of using asolvent for the asphalt which also affects the gutta percha is this-thatnot only is a good physical union between the first layer of asphalt andthe gutta ercha brought about, but the asphalt is also t erebyincorporated into the tissue to such an extent as to render its use moredesirable. This tissue is sensitive towards light and heat which tendsto harden it and render it brittle, while the tissue into which theasphalt has penetrated is beneficially afiected was to remain soft andflexible under the protective action of the asphalt. In addition, thiscompound of. gutta percha tissue and asphalt is a good dielectric initself.- Furthermore, this US$118 ma contain pin-holes at times, butthese pin-ho es are all sealed securely by the asphalt treatment.

The amount of carbon tetrachloride or other solvent used in practicewill va and depends on the physical characteristics of theparticulargrade of asphalt used. Suflicient should be used to make a freelyflowing solution. The gutta ercha tissue ma be in the form of strips 0the proper wi th for use in condensers of the rolled type. The strips oftissue may be sprayed with the solutlon, or may be floated across thetop of the liquid in a tank. In either case, after the coating is puton, the strip of tissue is run through a drier in order to evaporate thesolvent. After being dried, the asphalt side may .phalt in a solventwhich is common to asphalt and the tissue used, in coating the tissuewith the solution, and in evaporating the solvent.

In witness whereof, I hereunto subscribe my name this 15th day of March,A. D. 1929.

GODFREY S'l EERUP.

begiven a fine coating of talcum to prevent sticking during handling andto permit of the dielectric being wound up on reels. However, thedielectric ma be routed immediate- 1y to the winding mac ines to beformed into condensers, and in this case the coating of talcum may beomitted.

Having described my invention, what I consider to be new an desire tosecure by Letters Patent will be pointed out in the following'claims.

What is claimed is:

1. A dielectric comprising a carrier of thin tissue formed of gum of thegutta percha family and a relatively thick insulating coating of asphaltadhering to said tissue.

2. A dielectric comprising a layer of gum such as gutta percha, a layerof pure asphalt,

